I’m honestly surprised that this crossover hasn’t happened yet. Especially during the 90’s, when Marvel and DC were more open to crossovers, including the big Marvel Vs. DC miniseries that lead to the Amalgam Universe, where Wolverine and Batman were merged as Dark Claw (which was pretty awesome).
Back then Batman teamed with Marvel characters Spider-Man, Punisher, and Daredevil twice each. Yet they never teamed him up with Wolverine, who was arguably as popular as Spider-Man, as far as Marvel characters go. So it would seem like a natural choice for a comic. This would have been like printing money during the 90’s comic-book boom. And even now, after the success of the new Batman and X-Men films, the interest would be rather high.
Well, I think the premise I would use would be Ra’s Al Ghul‘s League of Assassins either joins forces with, or competes against The Hand, in some big worldwide terrorist plot. Independently, both heroes find out about the plot and try to stop it, with Batman coming up against The Hand and Wolverine coming up against Ra’s. I’d add a couple of other villains, The Hand hires Lady Deathstrike to kill Batman while Ras hires Lady Shiva to kill Wolverine. Eventually, the two heroes meet. I’d avoid the cliche of having them fight (realistically, Wolverine should be able to slaughter Batman rather easily), because they’ve both heard of each other before, and therefor know that they’re on the same side. There might be some conflict between the two, as Wolverine is willing to kill, while Batman is against it, but they’d work it out without coming to blows. And it would have to be a big double-sized issue, as I’d want the plot to be international, with the heroes traveling across the globe, to places like Japan and Saudi Arabia.
For the creative team, I think I’d pick Ed Brubaker as my ideal writer. He’s worked for both companies, and written both characters, so he should be able to handle it. For the art I think either Jim Lee or John Romita Jr. I know this will never happen, but I’d love it.